BUG: CBOR Transformation Breaks Script Integrity

[fallen-icarus]

I opened this issue under the cardano-hw-cli repo, but it looks like this library is used to actually transform the transaction (here). So the bug is actually here. If I am wrong about this, feel free to close this issue.

The TLDR is that transforming a transaction using a redeemer with internal fields will result in an invalid transformation. Submitting this transaction results in a ScriptIntegrity mismatch error. For example, transforming a transaction using the unit redeemer:

{"constructor":0,"fields":[]}

is fine, but transforming a transaction using this more complicated redeemer:

{"constructor":0,"fields":[{"constructor":1,"fields":[{"bytes":"c0f8644a01a6bf5db02f4afe30d604975e63dd274f1098a1738e561d"}]}]}

results in the ScriptIntegrity mismatch error upon submission.

You can verify this bug by trying to mint test tokens using the always succeeding minting policy which can be used with any redeemer:

{
    "type": "PlutusScriptV2",
    "description": "",
    "cborHex": "484701000022120011"
}

When I tested it, I got these results:

Redeemer	Transformed	Result
Unit	Yes	Success
Unit	No	Success
Complex	Yes	Fail
Complex	No	Success

This bug makes it impossible to use cardano-hw-cli to verify transactions involving smart contracts that use more complicated redeemers.

---

This is just a guess, but I am assuming the transformation is changing the redeemer's internal constructor index from 1 to 0 in order to comply with "integers must be as small as possible" (spec). The transformation should not touch the redeemer since the constructor index specifies which action is being taken.

EDIT: My guess was wrong. I tried using the complex redeemer with an internal constructor index of 0 and it still failed with a ScriptIntegrity error.